The present invention relates to a disc storage device for digital data as a peripheral device to one or more computer systems. More particularly, the present invention relates to a device in the form of a plurality of arms or stacks of read/write heads which are so positioned and operated as to minimize disc access time. The plurality of arms or stacks are combined with additional components which allow optimum utilization of such stacks. Furthermore, the freedom of access and other features inherent in the single stack system are retained.
Present disc systems are primarily of two basic types. One type of disc system is the fixed head type, i.e., with no movement of the read/write heads. Many heads are generally utilized and cost effectiveness is poor. Performance in most applications is also poor. The second type system is the moveable type, in which there is utilized a single stack or arm of read/write heads. In this second system, the mechanism electro-mechanically moves the heads transversely across the disc or platter surfaces between the periphery and the center portions of the discs. This second type system is more flexible than the fixed head type and there is much more storage capacity per head. Both of the foregoing prior art types of disc systems suffer from a common weakness, i.e., all read/write operations must wait until the specific portion of the particular disc surface that is to be operated upon revolves to coincidence with the appropriate disc head. Such operations result in a large latency ranging from virtually zero to one complete cycle, or more, of disc revolution, hence a bottleneck in input/output operations. U.S. patents which disclose such prior art systems include, for example, U.S. Pat. Nos. 3,219,979, 3,148,362, 3,973,274, 3,893,178, and 3,559,192.
By the present invention, there is provided an improved apparatus for minimizing disc access time in disc storage systems. The apparatus of the present invention includes a plurality of arms or stacks of read/write heads which are mounted around the periphery of the vertical disc pack. The use of such a plurality of stacks of heads has been found to markedly reduce disc access latencies. Additional features of the invention include: (a) means for prepositioning at least one of said stacks of heads while another stack is performing a read or write operation; and (b) means for simultaneously performing a separate read or write operation with each of at least two stacks of heads.
The present invention and its various embodiments are possible and effective irrespective of the basic characteristics of the particular disc system configuration. However, an optimization of all of the characteristics of the present invention and their integral relationship is possible and/or desirable. Such optimization primarily becomes a function of selecting the total power or capability of the new system that is required for each general application and configuring it appropriately.
By the present invention, the average disc access time for read or write operations will be reduced by at least 50% as compared to the present systems. Due to the improved features of the present invention as described above, the effective through-put capability and compute power of computer systems which employ the present invention will be tremendously increased. Data file and/or library structures will be greatly simplified, particularly for large information storage and retrieval systems. In addition, the general responsiveness of computer systems to user's needs will be greatly enhanced. The actual design of multi-user operating systems will be greatly simplified. I/O queueing operations, task or program scheduling, roll in or out of tasks, and the like will all be simplified. Larger programs may also be designed, in segments using the disc system as an extension of memory (non-executable). The cost effectiveness of computer systems will be greatly enhanced because of the many advantages as listed above.
A primary feature of the present invention includes the utilization of one or more additional arms or stacks of read/write heads. The various embodiments of the present invention are primarily intended for use with disc systems employing moveable heads. However, the present invention could also be employed in the case of a fixed head configuration. Such a configuration would effectively reduce the disc revolution latency.